1. Field of the Invention
This invention relates to the fabrication of semiconductor components such as integrated circuits. In particular, the use of silicon-containing polyimides as an oxygen etch barrier in a metal lift-off process and as an oxygen etch stop in the fabrication of multi-layer metal structures is disclosed.
2. Background Information
Improved materials and processes are required in advanced integrated circuit technology to meet the demands of fabricating high density interconnective multi-level metallurgy systems. In the lift-off method for fabricating fine metal lines, it is required that the contacting films maintain mechanical and interfacial integrity during the various processing steps; have requisite etch characteristics for compatibility with dry etch process schemes; and show the necessary thermal stability to allow high temperature metallization without any problem of outgassing, or image deformation.
The lift-off method for forming metallized structures generally involves the fabrication of a multi-layer stencil comprising a solvent removable polymer film as the base or lift-off layer on a substrate. This lift-off layer is sequentially overcoated with a thin oxygen reactive ion etch (RIE) barrier and a resist layer. The desired pattern in the resist is delineated by standard lithographic techniques and then replicated into the underlying barrier layer by the RIE process using CF.sub.4 ambient, followed by O.sub.2 to etch the pattern into the lift-off layer. Subsequent blanket metal evaporation and solvent soak (e.g., N-methylpyrrolidone (NMP)) is employed to accomplish the removal of the lift-off stencil, leaving the desired metal pattern intact.
The conventional O.sub.2 RIE barrier films as employed in the prior art include SiO.sub.x, Si.sub.3 N.sub.4, sputtered quartz, polydimethylsiloxane resins, and plasma-polymerized organosilicon films. Although the conventional barrier films have been employed effectively as masking layers for O.sub.2 RIE processes in multi-layer metal structures, there are several major drawbacks associated with the use of these materials as discussed below.
Relatively high temperatures, e.g., 200.degree. to 275.degree. C. are required for the deposition of inorganic films such as silicon oxide and silicon nitride. These high temperatures, however, can be detrimental to underlying organic polymer films resulting in reticulation and shriveling, in addition to the formation of debris at the organic/inorganic film interface. Furthermore, inorganic thin films invariably show high defect density (pinholes) which render them unacceptable for the fine line lithography required in the fabrication of high density integrated circuits. Inorganic barrier films in contact with organic polymer films such as polyimide also have problems of process induced stress cracking of the entire structure due to the mismatch in the coefficients of thermal expansion and the residual stress levels in inorganic versus organic films.
The solution coated thin films of spun-on glass utilized in the prior art, Franco, et al., U.S. Pat. No. 4,004,044 suffer from the problem of being susceptible to cracking above 250.degree. to 300.degree. C. when in contact with organic polymer films. Also, the glass-resin formulations have short shelf life and undergo formation of microgels which interfere with the film quality, resulting in a high level of defects.
Plasma polymerized organosilicon films for use as O.sub.2 RIE resistant layers as described in U.S. Pat. No. 4,493,855 to Sachdev et al., are free from the problems of the other prior art previously mentioned. However, the solution coated barrier films of this invention provide an inexpensive alternative requiring no special tooling and are specially suited for high volume manufacturing. A further advantage of the barrier films of this invention is the superior adhesion to a variety of organic and inorganic contacting layers without requiring any special surface preparation.
U.S Pat. No. 4,430,153 to Gleason et al., discloses the in-situ conversion of an alkyl polyamide/polyimide surface layer to a silicon-containing alkyl polyamide/polyimide layer. This process, however, is unsuitable for practical applications requiring metal lift-off structures due to interference of the processing solvents with the mechanical integrity of the solvent removable lift-off layers. Also, this treatment does not provide an effective O.sub.2 RIE resistance necessary for pattern transfer into the underlayer.
It is highly desirable to have an O.sub.2 RIE barrier which can be used in a manufacturing environment for fabrication of the sub-micron line widths required for high density interconnective metallurgy patterns, and which overcomes all the problems with the prior art.